con·cha 
(kŏngkə)
(kŏngkə)n. pl. con·chae (-kē′)
1. Anatomy Any of various structures, such as the external ear, that resemble a shell in shape. Also called conch.
2. Architecture The half dome over an apse.
[Late Latin, semidome, from Latin, mussel shell; see CONCH.]
conchal (-kəl) adj.